European patent document EP 0 349 188 B1 describes a device for the separation of blood into blood components, which has a blood collection bag which is connected via a first tube line to a primary bag, whereby the primary bag is connected via a further tube line to a satellite bag. A filter for the removal of leucocytes is disposed in the first tube line, which connects the blood collection bag to the primary bag. In order to obtain leucocyte-free components, a donor's whole blood is collected in the blood collection bag and transferred via the tube line containing the filter into the primary bag. The section of the tube line lying between the filter and the primary bag is then severed, whereby the severing point is sealed off. The primary bag is then centrifuged together with the secondary bag in order to separate the blood in the primary bag into two blood components. One of the two blood components is then transferred via the second tube line into the satellite bag. In this way, leucocyte-free blood components can be obtained after filtration of the whole blood. A decisive advantage with the known method is seen in the fact that centrifugation of the bag arrangement takes place without the filter and a mechanical strain on the filter is thus avoided.
The device for filtering whole blood known from European patent document EP 0 349 188 B1 is disadvantageous in that, after the completion of the filtration process, i.e., after the whole blood has ceased to flow from the blood collection bag into the primary bag under the influence of gravity, fluid can still remain in the leucocyte filter and in the respective tube line sections.
International Publication Number WO 91/17809 describes a filtering system which comprises a collection bag for receiving the filtered fluid, said collection bag being connected via a tube line, in which a filter is disposed, to a receiving bag containing the fluid to be filtered. The fluid to be filtered is transferred, under the influence of gravity, from the receiving bag via the tube line and the filter into the collection bag. In order to recover the fluid remaining in the filter and the adjacent tube line sections after completion of the filtration process, there is provided on the tube line a gas inlet upstream of the filter and a gas outlet downstream of the filter. After completion of the filtration process, gas is conveyed via the inlet into the system, said gas being carried away again via the outlet thereby expelling the fluid present in the system. In a preferred embodiment of the known filtering system, the gas to be conveyed into the system after completion of the filtration process is made available in a flexible bag, which is connected via a tube line to a gas inlet. The air carried away from the system is collected in a second flexible bag, which is connected via a second tube line to the gas outlet. In order to recover the fluid present in the system, the first bag is compressed after completion of the filtration process, as a result of which the gas flows into the system thereby expelling the fluid. The drawback is that the known filtering system with the gas inlet and the outlet is relatively costly to produce and difficult to manage.
There is also known from International Publication Number WO 03/064000 A1 a filtering device which comprises a filter. The filtering device has a tube line, which connects a receiving bag to a collection bag and into which a filter is incorporated, which is divided by a filter material into a first and second chamber. Moreover, the device has another bag, which is in a flow connection with the first and second filter chamber respectively via an air inlet and outlet line. Disposed in one of the two lines is a non-return valve, which permits a passage of fluid only in the direction of the first filter chamber. The bag serves for deaeration of the system when the fluid is transferred from the receiving bag into the collection bag. The drawback is that the incorporation of the bag with the air inlet and outlet lines makes the handling of the system difficult.